Infusion device with disposable elements

ABSTRACT

An infusion device with a disposable administration set which is inexpensive to manufacture. In the preferred embodiment of the present invention the disposable administration set has a plurality of elongated cam followers connected to a plate assembly, wherein the cam followers are displaced in a predetermined sequence and forced against a delivery tube by cam means driven by rotary drive means. The disposable administration set is injection molded as a single integral piece. The disposable administration set includes adjustment spacers disposed between the plate assembly and the cam followers which adjust the distance between them to keep the device accurate. In the preferred embodiment of the present invention the cam means are configured to provide fluid delivery at a consistent and uniform rate.

This application is a division of application Ser. No. 194,865, filed5/17/88.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a medication infusion device foradministering fluid to patients and more particularly to an improved,ambulatory infusion device with a disposable administration set which isinexpensive to manufacture, convenient to operate and which ensuresfluid delivery at a consistent and uniform rate.

2. Description of the Prior Art

As a result of the ongoing need for improved health care, there is acontinuous effort with regard to administering intravenous fluid topatients. As is well known, medication dispensers and infusion devicesare used for infusion of predetermined amounts of medication into thebody of a patient. Various types of medication dispensers employingdifferent techniques for a variety of applications are known to exist.Some existing infusion devices utilize a series of diaphragms which rollup and down inside cylinders in response to pistons located within thecylinders. Such devices, for example, as disclosed in U.S. Pat. Nos.4,236,880, 4,277,226, 4,391,600 and 4,410,322 are characterized byrelatively complicated operational procedures and numerous manufacturingand maintenance adjustments to ensure proper operation of the loadingand valving functions.

Other existing infusion devices employ a finger type pump unit havingfingers which are moved in predetermined sequence to squeeze a feedingtube to infuse predetermined amounts of medication continuously andcyclically into a patient. Such a prior art device is disclosed in U.S.Pat. No. 4,479,797.

In many cases it is of critical importance to provide preciselycontrolled and consistent flow rates of intravenous fluid to patients.This need for more controlled IV flow rates is only partially fulfilledby the above-mentioned displacement pumps. The finger type displacementpump unit as disclosed in U.S. Pat. No. 4,479,797 includes a pluralityof elongate fingers which are depressed by an equal number of associatedcams rotating about a shaft which is driven by a motor. A feeding tube,when placed between the fingers, is squeezed by the fingers to infuseliquid medication into a human body. The elongate fingers comprise acentral finger and two side fingers arranged on either side. In such adevice the side fingers completely squeeze or collapse the feeding tubeat the designated point of contact on either side, and the centralfinger is shaped for squeezing the feeding tube and pumping medicationover the length of tube between the two points, providing a pulsatileflow of fluid. During the time that the downstream side fingercompletely squeezes the feeding tube, while the pumping portion of thetube is filling from an upstream supply, the flow of fluid to thepatient is completely obstructed.

Completely obstructing the flow of medication for periods of time andproviding pulsatile flow is often a clinically unsatisfactory andundesirable condition since a patient is deprived of medication forperiods of time. Additionally, fluid is delivered at non-uniform rates.Sometimes, the possibility exists at low flow rates for a catheter todevelop a blood clot due to lack of flow. This may also result in anoccluded tubing, so that the patient may be deprived of neededmedication for several hours. This condition is especially likely in ahome environment which seldom has around-the-clock clinical staffing formonitoring patients. Thus, it is desirable to have an infusion devicewhich delivers fluid to a patient at a constant and uniform rate.

Some prior art devices, in an attempt to provide non pulsatile flow offluid, incorporate additional pulsation correction cams and camfollowers. The correction cams are designed to even out overall flowfrom the pump through simultaneous pumping actions of multiple cams.This solution is undesirable in view of the numerous parts involved.Infusion devices utilizing piston valves and cylinders are also known toprovide uniform flow; however, they do so at the expense of crudevalving techniques and complex mechanisms. Thus it is desirable to havean infusion device utilizing a relatively simple technique of providingnon-pulsatile flow.

As is well known, disposable equipment for medical applications isdesirable so as to maintain a germ-free environment to prevent thetransfer of infection especially where cost prohibits cleaning andsterilization after each use. Prior art devices employing a series ofdiaphragms rolling within cylinders have utilized disposable diaphragms.The disposable diaphragms, however, are flimsy and thus require a verycomplex loading mechanism. Prior art devices having finger type pumpunits, for example, as disclosed in U.S. Pat. No. 3,658,445, have only adisposable tube assembly. This has limited advantages, since the camfollowers, which are not a part of the disposable assembly, are notrenewed with each replacement. U.S. Pat. No. 4,479,797 discloses otherdisposable elements. Since the cam followers are repeatedly flexed andfatigued as a result of being depressed by the rotating cams, it isdesirable to have them renewed with every new installation to ensureproper functioning.

Thus, it is desirable to have a disposable administration set, includingthe pumping tube itself, a base plate against which the tube isdepressed, and the cam followers. With such an arrangement, the systemoperates reliably and accurately over a longer period of time becauseits major pumping components are replaced with each use. Anotherimportant consideration for disposable elements is cost, since clinicalapplication of disposable administration sets requires that theadministration sets be regularly replaced. Typically, such sets arereplaced every 24 to 48 hours, and seldom remain in use longer than oneweek. This frequent replacement interval should ideally be fulfilled byan inexpensively molded, disposable, mechanism which would normally notlast the years of service life expected from the pump itself.

Furthermore, it is desireable to have a disposable administration setwhich is easy to load and unload to minimize operator errors. Thesefactors can be very important in a clinical situation when a few extraseconds may be critical to a patient's life. Typically, prior artdevices require several steps to accomplish the task of loading andunloading. Additionally, it is beneficial to pinch off the delivery tubeand obstruct fluid flow prior to loading or unloading the administrationset.

It is also desireable to have an efficient but inexpensive occlusiondetection system. Some prior art devices incorporate a pressuretransducer and diaphragm assembly to monitor fluid pressure as anindication of occlusion. Such an occlusion detection technique isundesirable in view of the complexities and cost involved. Prior artdevices utilizing pistons and cylinders detect occlusion by utilizing aswitch mounted within the cylinder. When the pressure reaches a certainvalue the rotating diaphragm causes the switch to be depressed. Theswitch may also be mounted against the tubing such that the switch isactivated when the tubing expands as a result of increased pressure dueto an occlusion.

SUMMARY OF THE INVENTION

Briefly stated, the present invention is an improved, ambulatoryinfusion device having a disposable administration set which isinexpensive to manufacture and a pumping mechanism which provides aconsistent and uniform fluid flow.

The infusion device comprises an administration set having a pluralityof cam followers which are depressed in a predetermined sequence by aplurality of associated rotating cams. The cam followers squeeze adelivery tube to dispense fluid which is intravenously infused into apatient's body. The rotating cams are mounted to an axle shaft driven bya motor. The disposable administration set further comprises a plateassembly to which the cam followers are attached. The cam followersforce the delivery tube against the plate assembly to pinch off thedelivery tube or force fluid to flow through it. In the preferredembodiment of the present invention the administration set isadvantageously disposable and inexpensive to manufacture. In accordancewith one feature of the present invention the cam followers are allmolded together as one piece. Alternatively, the cam followers may alsobe molded as one piece with the plate assembly, provided that a hinge ismolded to connect the cam followers with the plate assembly. Thisprovides a cost effective assembling technique which allows the camfollowers and plate to be replaced regularly at minimal cost.

Since the cam followers are instrumental in controlling the amount offluid dispensed, the thickness of the cam followers is a criticaldimension which directly affects the degree of tube compression, andthus the cross sectional area of the delivery tube. Because somevariations in thickness can be expected from one molded part to the nextdue to normal molding process variations, the invention utilizes gapcorrection spacers which counteract these thickness variations. The gapcorrection spacers fit between the plate and the support for therotating cam, and thus adjust the distance between the cam and theplate. If the cam follower assembly varies in thickness, for example dueto change in the pressure of an injection molding machine, both the camfollowers and the gap correction spacers vary by the same amount,because they are molded as a single unit. Since an increase in thicknessof the gap correction spacers results in an increase in the deliverytube gap, while an increase in the thickness of the cam followersresults in a decrease in the delivery tube gap, the net effect is nochange in the delivery tube gap. It is this correction technique thatallows the followers to be injection molded without sacrificing theaccuracy of the fluid delivery.

An additional feature of the invention allows the use of a low costmolded pressure plate assembly. Springs are used to force the face ofthe tubing retainer plate against the gap correction spacers. Thesesprings, of course, must be stiff enough to be unyielding as the camssqueeze the delivery tube. By floating the plate on such springs,changes in thickness from plate to plate due to molding variations donot change the tubing gap from part to part. This is another importantpart of the invention which allows an easily loaded and inexpensivedisposable administration set to be used without sacrificing performanceor accuracy.

The plate referencing system and the gap correction spacers describedabove are adapted to increase the accuracy of the delivery system. Incooperation with the gap correction spacers, a channel in the pumpingsystem receives the retainer plate and the spacers. The springsmentioned above are mounted in this channel and force the disposableassembly against a reference shoulder within the channel. This shoulderallows an easily manufactured dimensional precision to accurately definethe tubing gap. The critical dimensions are the cam radius itself andthe distance between the cam axis and the plate referencing shoulder.These two dimensions can be precisely controlled in the manufacturingprocess and they will not change significantly with time or usage.

Another feature of the present invention exists in the ability todeliver fluid at a consistent and uniform rate. The pumping mechanismincludes an axle shaft and a plurality of cams mounted thereto. As theaxle shaft rotates, the cams force the cam followers to squeeze thetubing and thereby displace a certain volume of fluid which is thenforced out of the pump. The cams are structurally adapted such the eachincremental angle of revolution displaces the same amount of fluid. Thisis facilitated by a non-linear cam design which provides a non-linearchange in the delivery tube gap. The change in cross sectional area ofthe delivery tube caused by a given change in the gap depends on thetube gap at the start of the change. The cam non-linearity is designedto correlate with this change.

The present invention utilizes two pumping cams and two pumping camfollowers, which function such that, at any point in time, one of thetwo pumping cams is always pumping. The two pumping cams comprise aprimary pumping cam associated with an upstream segment of the deliverytube and a secondary pumping cam associated with a downstream segment ofthe delivery tube. The primary pumping cam is wider than the secondarypumping cam, so that it can displace sufficient fluid during its pumpingstroke to deliver fluid external to the pump and at the same timedeliver fluid to the section of the tubing beneath the secondary pumpingcam to allow it to fill. The secondary pumping cam is narrower, since itonly needs to deliver fluid external to the pump. The present inventionadditionally utilizes pinching cams and pinching cam followers, whichopen and close the delivery tube to allow the pumping action to functionproperly. The pinching cams comprise an inlet pinching cam associatedwith the upstream segment of the tube and an outlet pinching camassociated with the downstream segment of the tube. Thus the pumping camfollowers, acted upon by the pumping cams, control the rate of fluidflow, while the pinching cam followers acted upon by the pinching cams,operate as valves for the pump. Such a configuration allows one segmentof the delivery tube to fill with fluid while another segment of thedelivery tube is pumping, thus providing a continuous and uniform fluidflow.

In still another feature of the present invention the disposableadministration set of the infusion device is less prone to operatorloading errors. This is accomplished through a reduced number ofrequired operations and a reduction in the complexity of the operations.This is facilitated by providing channels extending along the length ofthe walls of a housing structure of the infusion device. These channelsslidingly receive the disposable administration set in a simple, singleinsertion step. Additionally, since the disposable administration setincludes the delivery tube retainer plate and cam followers, theposition of the delivery tube relative to the tubing retainer plate andcam followers is established in a manufacturing operation which can beclosely controlled. Assemblers are not under the stress of a clinicalsituation and they specialize in the proper assembly of the disposableadministration set. Good manufacturing procedures provide additionalchecking systems to insure that the tubing is properly loaded and thatthe administration set properly assembled. These practices are notpossible in a clinical environment.

The pump of the infusion device is non-functional when loaded with analien disposable administration set. Alien administration sets may havecharacteristics which are not suitable for safe operation of the fluiddelivery system, and may operate outside of specified tolerance limits.The pump will not operate with a standard piece of delivery tube,because it requires an administration set with cam followers and apressure plate.

Another feature of the present invention is a provision for detecting anocclusion in the downstream fluid path. The cams which squeeze thetubing are rotated by a DC motor having a predictable torque-to-currenttransfer function. By monitoring the current to the motor, the amount oftorque required to maintain a desired camshaft velocity can be measured.With knowledge of the motor torque required to advance the cam at eachposition along its rotation, against a normal fluid back-pressure, andcomparing this torque with the actual measured torque,higher-than-normal pressure in the delivery tube can be sensed. Ifdesired, a calculation can be made to determine the torque normallyrequired to rotate the cam. This torque calculation takes into accountthe pressure exerted by the tube against the cam face, the effectiveradius of the cam-follower contact point, and the coefficient offriction of the cam-to-follower contact for each cam rotationalposition. This calculation is undertaken for each cam, to yield a totalaccumulated torque value. This total torque profile is stored in amemory device to be read out and compared with the actual torque formonitoring abnormally high pumping pressures.

Alternatively, the memory may be loaded with actual D.C. current dataread during a previous operation of the pump with normal pressure. Thisprofile is unique to the particular mechanism and instrument in which itis installed. The profile is a current waveform sampled at specificangles of revolution of the pumping system. The waveform is sampled andstored during the actual operation of the pump under controlledconditions, i.e. specific output pressure, specific temperature, etc.During later operation of the pump, these stored values are periodicallycompared to the actual operating current and an alarm is signalled ifthe difference between these two values exceeds a specified tolerance.

The control system also has access to the current operating temperaturewhich may be used to adjust the allowable tolerance for changes in theoperating temperature. The control system may also have access to datastored on the disposable administration set which indicates particularinformation related to manufacturing variances, such as coefficient offriction, stroke volume, tubing gap, tubing wall thickness and diameter,etc. This information may also be used to determine the appropriatealarm point. The information may be stored on the disposableadministration set so that it may be read by the instrument during thesliding operation of loading the set.

The present invention uses a minimal number of parts and dissipates aminimal amount of energy. The disposable concept which includes the camfollowers and the pressure plate allows for a high precision pumpwithout complicated assembly or loading mechanisms. The set loading andretaining channels allow precise positioning of the tubing, followers,and pressure plate without any adjustments or complicated, bulky, orexpensive mechanisms. The disposable administration set results in anoverall fluid delivery system which is small, lightweight, andambulatory.

The design of the disposable administration set in combination with theplate referencing channels allows a sliding operation in order to loadthe set. This sliding operation allows for the transfer of informationfrom the disposable administration set to the instrument from fixedsensors. These sensors may be optical, magnetic, or some othertechnology. The preferred embodiment uses optical sensors to readoptically coded information from a label on the administration set. Thiscapability permits the instrument to be programmed from the informationincluded on the label. The instrument operator is thus free fromprogramming tasks, which would be difficult in a clinical environment.Programming information can be added to the administration set duringthe preparation or prescription of the medication to be delivered. Theunique sliding operation makes this programming simple and costeffective in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the present invention is illustrated in andby the following drawings in which like reference numerals indicate likeparts and in which:

FIG. 1 is a perspective, exploded view illustrating an infusion devicehaving a disposable administration set in accordance with the presentinvention, in particular showing the simple loading and unloadingoperation of the disposable administration set.

FIG. 2 is a perspective view illustrating the disposable administrationset of the present invention.

FIG. 3 is a cross section view taken along the line 3--3 of FIG. 1.

FIG. 4 is a plan view illustrating the single-piece cam of theinvention.

FIG. 4a is a cross section view taken along the line a--a of FIG. 4illustrating the contour of the outlet or secondary or downstreampumping cam of the present invention.

FIG. 4b. is a cross section view taken along the line b--b of FIG. 4illustrating the contour of the outlet pinching cam of the presentinvention.

FIG. 4c is a cross section view taken along the line c--c of FIG. 4illustrating the contour of the inlet or primary or upstream pumping camof the present invention.

FIG. 4d is a cross section view taken along the line d--d of the presentinvention illustrating the contour of the inlet pinching cam of thepresent invention.

FIG. 5 is a plan view illustrating a cam follower and spacer assembly ofthe present invention.

FIG. 6 is a side elevation exploded view illustrating the cam followerand spacer assembly and the plate assembly.

FIG. 7 is a graphical representation of the cam radii versus the angleof cam rotation of the present invention.

FIG. 8 is a graphical representation of the tubing ID gap versus theangle of cam rotation of the present invention.

FIG. 9 is a graphical representation of the total torque versus theangle of cam rotation of the present invention.

FIG. 10 is a block diagram of the occlusion detection system of thepresent invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates the infusion device 10 of the preferred embodiment ofthe present invention for administering intravenous fluid at aconsistent and uniform rate. The infusion device 10 is designed to besmall, lightweight and ambulatory. The infusion device 10 includes adisposable administration set 12 having a plurality of cam followers 42which are displaced in a predetermined sequence when depressed by apumping mechanism 64 to squeeze a delivery tube 36 for dispensing fluid.The pumping mechanism 64 is driven by a commercially available motor 11(not shown). Mounted within a housing structure 66, the disposableadministration set 12 loads easily into the housing structure 66.Oriented directly above the housing structure 66 is an optional fluidreservoir 60 which provides a continuous flow of fluid to the inlet ofthe delivery tube 36 for dispensing and infusing fluid into a patient'sbody. Alternatively, the fluid delivery tube 36 may connect to anexternal reservoir (not shown), or the reservoir 60 may be located atother positions on the assembly.

The housing structure 66 comprises a rectangular chamber 67 surroundedby side walls 68 and a rear wall 69. The floor of the rectangularchamber 67 drops into a recess 70 towards the front end. The pumpingmechanism 64 is located within the recess 70. Extending throughout thelength and parallel to the base of each of the side walls 68 is a narrowchannel 72 having a lower shoulder 73. The disposable administration set12 slides within the channels 72. As best seen in FIG. 3, each of thechannels 72 includes a spring-biased ball assembly 75. The disposableadministration set 12, while being manually inserted into the channels72, depresses the spring assemblies 75. After insertion of the set 12,the spring assemblies on either side bias the disposable administrationset 12 against the shoulders 73 of the channels 72, holding thedisposable administration set 1 2 accurately in position. In operation,the disposable administration set 12 is manually loaded into theinfusion device 10 in a simple sliding operation. As the administrationset 12 slides into the infusion device, the cam followers 42 aregradually pushed against the delivery tube 36 by the pumping mechanism64.

FIGS. 2 and 6 illustrate the disposable administration set 12 of thepreferred embodiment of the present invention. The disposableadministration set 12 is formed from rigid plastic or the like, andincludes a tubing retainer plate assembly 14 which may advantageously beinjection molded as a single piece.

The tubing retainer plate assembly 14 includes a tubing retainer plate16 having a flat tube-contacting surface and a cam follower retainer 20projecting normal to this surface at one end. The cam follower retainer20 terminates in a an overhanging latch 24 projecting substantiallyparallel to the retainer plate 16. The latch 24 serves as a lockingmechanism for holding the cam followers 42 in position, adjacent thetube 36 prior to insertion of the administration set 12 into the housing66. During insertion of the administration set 12 into the channels 72,the cam followers 42 are depressed by the pumping mechanism 64. Thiscauses the cam followers 42 to move away from the latch 24. Thusinsertion of the administration set 12 automatically moves the camfollowers from a standby position, against the latch 24, to an operatingposition pushed against the tube 36.

As best seen in FIGS. 2, 5 and 6 the disposable administration set 12further includes a cam follower and spacer assembly 40. In the preferredembodiment of the present invention the cam follower and spacer assembly40 may also be injection molded as a single piece independent of thetubing retainer plate 16. Alternatively, the cam follower and spacerassembly 40 may be molded as one piece with the tubing retainer plateassembly 14 provided that a hinge is molded to connect the cam followerand spacer assembly 40 to the tubing retainer plate assembly 14. The camfollower and spacer assembly 40 includes two gap correction spacers 44in the form of elongated extending finger-like projections which flankthe tubing retainer plate 16 on either side (as best seen in FIG. 2).Since the cam followers 42 are instrumental in controlling the amount offluid dispensed, the thickness of the cam followers 42 is a criticaldimension which directly effects the volume of the delivery tube 36. Theaccurate pinching of the delivery tube 36 is necessary to allow adesired flow of fluid through the available passage. However, due totypical molding process variations such accuracy may not be possible.The gap correction spacers 44 advantageously counteract for thesethickness variations. During the molding process, the thickness of boththe cam followers 42 and the gap spacers 44 will vary by the sameamount, because they are formed in the same mold cavity. Thus, anymolding variations, such as those due to mold temperature or pressure,will affect both of these parts identically.

Referring to FIG. 3, it will be seen that, after insertion of theadministration set 12 into the housing 66, the dispensing tube 36 ispositioned immediately below the spring-biased retainer 75. Thespring-biased retainer 75 holds the administration set accurately inplace against the shoulders 73 (as best seen in FIG. 1) as describedearlier. The cam followers 42 are pushed against the tube 36 by aplurality of cams 85, one of which is shown in FIG. 3. Pumping isaccomplished, as will be described below, by squeezing the tube 36.

The gap correction spacer 44 rests between the plate 16 and the shoulder73 (as best seen in FIG. 1). Thus, if the spacer 44 is thicker thannormal, the plate 16 will be positioned further from the cam 85 thannormal. However, in this case, as explained above, the cam followers 42will also be thicker than normal, offsetting the effect of the thickerspacer 44. It is advantageous, in accomplishing this self correction,that the thickness of the spacer 44 be the same as that of the activepart of the follower 42, so that they will vary identically inthickness.

The plurality of cam followers 42 as best seen in FIG. 5, includes aninlet pincher cam follower 43, a primary, upstream, inlet pumping camfollower 46, an outlet pincher cam follower 48, and a secondary,downstream, outlet pumping cam follower 50. Each of the cam followers 42are attached to the cam follower and spacer assembly 40 by flexible camfollower arms 54. Each of the cam followers 42 are displaced toward thedelivery tube 36 in a predetermined sequence. The inlet pincher camfollower 43 and the outlet pincher cam follower 48 deform the fluiddelivery tube 36 to close it off, and thus act as valves. The primarypumping cam follower 46 and the secondary pumping cam follower 50 pumpthe fluid through the delivery tube 36. The primary pumping cam follower46 which contacts the upstream segment of the delivery tube 36 isapproximately twice the width of the secondary pumping cam follower 50,and it thus squeezes twice the length of tubing. This facilitatesdisplacement of enough fluid during a pumping stroke for deliveringfluid external to the pump and at the same time delivering fluid to thedownstream segment of the fluid delivery tube 36, beneath the follower50, to allow it to fill. Thus, as the follower 46 is being advancedtoward the tube 36, the follower 50 is being withdrawn. The fluiddisplaced by the follower 46 fills the tube 36 as it is released by thefollower 50, and also supplies enough fluid to continue the outflow fromthe pump.

Referring now to FIG. 4, the pumping mechanism 64 which provides acontinuous and uniform flow will be described. The pumping mechanism 64comprises a cam assembly 84 and an axle shaft 86. In the preferredembodiment, the cam assembly 84 is preferably formed and machined from asingle piece of metal. Alternatively, the cam assembly 84 may be cast,and later machined. As shown, the assembly 84 includes a centralaperture 83 to accommodate an axle shaft 86. The shaft 86 may include aflat 86a to couple the shaft 86 to a motor. The axle shaft 86 rotateswithin bearings which are in turn mounted in two apertures formed withinthe walls 68 as best seen in FIG. 1. The axle shaft 86 driven by themotor provides rotation to the cam assembly 84. The cam followers 42subsequently are displaced in a predetermined sequence, as describedbelow, thereby squeezing the delivery tube 36 and dispensing a specifiedvolume of fluid.

The cam assembly 84 is specifically designed such that each incrementalangle of revolution displaces the same amount of fluid. The cam assembly84 includes the plurality of spaced cams 85. The plurality of spacedcams 85 include an inlet pincher cam 87, a primary, upstream, inletpumping cam 88, an outlet pincher cam 90 and a secondary, downstream,outlet pumping cam 92. The inlet pincher cam 87 and the primary pumpingcam 88 are operably associated with the inlet pincher cam follower 43and the primary pumping cam follower 46, respectively. Similarly, theoutlet pincher cam 90 and the secondary pumping cam 92 are likewiseoperably associated with the outlet pincher cam follower 48 and thesecondary pumping cam follower 50.

Referring to FIGS. 4b and 4d the inlet pincher cam 87 and the outletpincher cam 90 are described. The inlet pincher cam 87 and outletpincher cam 90 operate as valves for the pumping action. The surfaces ofthe pincher cams 87,90 are contoured such that between specifiedrotational positions either the upstream or the downstream segment ofthe tube 36 is pinched off to obstruct fluid flow.

Referring to FIGS. 4a and 4c, the primary pumping cam 88 and thesecondary pumping cam 92 include active pumping surfaces which areuniquely contoured so that the fluid delivery tube 36 is squeezed insuch a manner that a constant speed of rotation of the axle shaft 86results in a uniform or constant displacement of fluid volume from theappropriate segment of the fluid delivery tube 36. To accomplish thisresult, the primary pumping cam 88 and the secondary pumping cam 92surfaces are contoured based upon the following principles andcalculations.

The equation defining the volume of a cylindrical tube with 1representing the length and d the inside diameter is as follows:##EQU1##

The equation defining the volume of an elliptical tube with grepresenting the inside edge diameter or minor gap and L representingthe portion of the cam in contact with the cam follower is as follows:##EQU2##

Since the circumference of the tube 36 remains relatively constant whenthe tubing is deformed from a cylindrical shape into an elliptical shapeby the cam followers 42, the cylindrical circumference equals theelliptical circumference.

    C.sub.eli =C.sub.cyl

Additionally the circumference of a cylinder and an ellipse are definedas C_(cyl) =πd and C_(eli) =2×L+π×gg, respectively.

Thus since the circumference remains constant throughout the deformationprocess of the delivery tube 36, the two circumferences may be equatedas follows:

    π×d=2×L+π×g

Solving for L

    L=(π×d-π×g)/2

and substituting for area

    area=g×L+π×g×g/4=g×(π×d-π×g)/2+π×g×g/4

    area-(π/2)×g×d-(π/4)×g×g

considering that g=d as the total area displaced and breaking that totalarea into 100 equal area increments

    total area=π×d×d/4

    and the

    incremental area change=π×d×d/400

and then solving for the 100 g values corresponding to each of the 100incremental area increments

    area 1=(π/2)×g×d-(π/4)×g×g=π×d×d/400

and solving for g given the constant cylinder d value and letting

    K=π×d×d/400 for simplification

and letting π/4=c for simplification

    2×c×d×g-c×g×g-k=0

and solving for the second incremental area

    2×c×d×g-c×g×g-×k=0

and calculating the remaining 98 equal area increments.

An incremental part of the cam rotation is selected for filling and theremaining part of the rotation will be for pumping. For example, if 180°is selected for pumping, then each incremental area change will occur in1.8° increments such that the g for the first incremental area willoccur at 1.8 degrees, the g for the second incremental area will occurat 3.6 degrees, etc. Finally, the g for the 100th area will occur at 180degrees. The cam radiuses at each increment can then be calculated bysubtracting the required g value from the displacement between thecenter of the cam to the face of the plate assembly minus the camfollower thickness minus 2 times the tubing wall thickness plus the gapspacer thickness.

Using this derivation, it is possible to generate the proper cam pumpingprofile for any combination of tube diameter, cam spacing, tube wallthickness, and cam-degrees of pumping rotation.

The relationship between the cam radius and the tubing gap isalgebraically proportional only when the cam radius in constant. As thecam radius changes, the effect of the approximately horizontal surfaceof the follower, contacting the changing cam surface makes it necessaryto take the phase and amplitude into consideration. For example, arapidly increasing cam surface results in a gap change that leads theactual radius change. Likewise, a rapidly decreasing cam radius resultsin a gap change that lags the actual radius change. The amount of changein phase is a function of a ratio of the beginning and ending cam radii.

The present invention utilizes approximate predicted phase changes basedon calculations, of the ratio of the beginning and ending cam radii,relative to the rotational positions of the cam. This effect is moresignificant in the case of the rapidly changing pincher cams which arecharacterized by transitioning phase changes of approximately 35degrees. Thus, once the cam profiles and approximate rotationalpositions of each cam are selected, the actual gaps are numericallycomputed as described. For each degree of rotation, each radius has avertical component which is computed by multiplying the actual radiuslength by the cosine of the angle that is formed by that radius relativeto a vertical line. The vertical line passes through the center of theaxle shaft and is approximately normal to the surface of the camfollower. The vertical component of each radius thus changes as the camrotates about its axis. Since the follower is formed to contact the camsurface in an approximately downward direction, for a particular degreeof rotation of the cam, the cam follower will contact the cam surface atthe radius which has the greatest positive vertical component. Theactual radius of contact at each degree of rotation is determined bynumerically computing the radius with the greatest vertical component ateach degree of rotation.

Referring to FIGS. 4 and 7 the operation of the cams 85 relative to thegap of the delivery tube 36 will be described. The cam assembly 84, asseen in FIG. 4, rotates about the axle shaft 86 acts through the camfollowers upon the delivery tube 36 positioned directly beneath the camassembly 84. As best seen in FIG. 7, between the rotational positions 0degrees and 200, degrees the inlet pincher cam 87, indicated by a curvetrace 87a, forces the inlet cam follower 43 to pinch off the upstreamsegment of the tube 36 to prevent fluid flow back into the reservoir 60.While the upstream segment of the tube 36 is pinched off, the primarypumping cam 88 progresses through a gradual pumping stroke lasting from0 degrees to approximately 175 degrees, indicated by the curve 88a. Thisdisplaces the inlet pumping cam follower 46 against the tube 36 tosqueeze enough fluid to the downstream segment as well as external tothe pump to continue to provide a uniform and consistent flow while thetube 36 beneath the secondary pumping cam 92 is filling. This filling iscaused by a reduction in the diameter of the cam 92 through thisrotational segment, as shown by curve 92a.

Once the downstream segment of the tube has been filled with fluid (atapproximately the 180 degree rotation point), the outlet pincher cam 90closes and remains closed between the rotational angles 200 degrees to340 degrees, indicated by the curve 90a. This forces the outlet camfollower 48 to pinch off the downstream segment of the delivery tube 36.When the cam 90 pinches the tube 36 at approximately the 180 degreerotational position, the cam 87 rotates to a reduced diameter regionwhich extends between approximately 220 degrees and 340 degrees. Thisopens the tube 36 beneath the cam 87, as shown by curve 87a, to allowfluid to flow from the reservoir 60 to the portion of the tube 36 whichunderlies the cam 88, so that this tube portion may fill. This allowsthe upstream segment to fill in response to a gradual reduction in theradius of the cam 88, as shown by the curve 88a between 220degrees and340 degrees. During this segment, the secondary pumping cam 92,indicated by the curve 92a, depresses the secondary cam follower 50against the tube 36 dispensing fluid external to the pump.

Referring to FIG. 8, the affect of the cams 85 on the tubing gap duringtheir rotational movement is shown. The curves of FIG. 8 are thussomewhat inversely proportional to the curves of FIG. 7, since anincrease in cam radii causes a decrease in the corresponding tube gap,taking into account the fact that the gap change leads the actual radiuschange. The upstream segment of the tube 36, indicated by the curve 87bis completely pinched off between the rotational positions 340 degreesand 200 degrees. The primary pumping cam 88, as described above, reducesthe gap beneath it to expel fluid until it reaches a rotational angleposition of 175 degrees, as indicated by the curve 88b. The gap of thetube 36 beneath the cam 92 is gradually increased during this segmentbetween 0 180 degrees, so that the tube 36 beneath the secondary pumpingcam 92 will slowly fill with fluid.

Once the downstream segment of the tube 36 has been filled, the outletpincher cam 90 causes the downstream segment to be pinched off asindicated by the curve 90b so that the secondary pumping cam 92 candeliver fluid external to the pump. The tubing gap beneath the cam 92varies as indicated by the curve 92b during the pumping stroke (175degrees to 360 degrees) of the secondary pumping cam 92.

Referring to FIG. 9, it can be seen that the total torque required fromthe motor to rotate the cam depends upon (1) the cam position, and (2)the back-pressure of the fluid being pumped. The lower curve 101 showsthis total torque with low back pressure, while the curve 103 shows thetorque required to pump at a relatively high back pressure. The curvesof FIG. 9 are derived empirically, or may be calculated. In either casewhen the cam followers 42 have pinched off the tube 36 and actuallydeform the wall thickness of the tube 36, a torque spike is required.When the tube 36 is released a reverse torque spike is generated. Forexample, at the rotational position of 200 degrees, when both the inletpincher cam 87 and the outlet pincher cam 90 are pressed against thetube 36, a torque spike 150 is observed. A negative spike 152 indicatesthe torque applied by the tube 36 as a result of the materialdeformation. If the cam 84 is rotated at a constant speed, the torquespikes of FIG. 9 will result in current spikes in the DC currentrequired for motor rotation.

Referring to FIG. 10, a block diagram of the occlusion detection systemused in the infusion device 10 will be described. The DC motor 11 whichrotates the axle shaft 86 has a predictable torque-to-current transferfunction. By monitoring the current to the motor 11 for a proportionalsignal thereof, the amount of torque required to maintain a constantvelocity of the axle shaft 86 can be measured. With knowledge of themotor current required to advance the pumping mechanism 64 at eachposition along its rotation, against a normal fluid back-pressure, andcomparing this current with the actual measured current,higher-than-normal pressure in the delivery tube 36 can be sensed. Acalculation can be made to determine the current normally required torotate the pumping mechanism 64. This current calculation takes intoaccount the pressure exerted by the delivery tube 36 against the camfaces, the effective radius of the cam-to-follower contacts for each camrotational position. This calculation is undertaken for each cam, toyield a total accumulated torque value. Alternatively, the cam can berotated against a normal back-pressure to empirically measure thecurrent required for normal operation. This current waveform isproportional to the torque shown in FIG. 9 as the curve 103. The currentcan be sensed for example at each 1 degree of rotation and stored in amemory 100. During subsequent clinical use of the pump, the actualcurrent required to rotate the motor is monitored by a current sensor104 and converted to digital format by an A/D converter 105 to becompared by a comparator 106 with the current profile stored in thememory device 100. A shaft encoder 101 is used to address the memory 100to output the appropriate current level for a particular rotationalposition. The difference between the actual current and the storedcurrent profile, is subsequently compared with a reference constantindicating a critical situation which is stored in a memory 108. Forexample, the memory 108 may provide the digital equivalent for thecurrent increase which would be expected if the back pressure increasedby 5 psi. This level may indicate the likelihood that the output isoccluded and an alarm should be sounded. If the error signal fromcomparator 106 exceeds the reference value, from the memory 108 acomparator 110 automatically may trigger an audio alarm means. Thememory 108 may store plural alarm levels which are applicable atdifferent temperatures. Thus, the allowable tolerance of the referenceconstant is temperature dependent. For example, temperature may affectthe pliability of the delivery tube 6, in which case, the referenceconstant may be adjusted to allow a larger divergence between expectedcurrent and actual current when the tube is cold, and thus more rigid.Additionally, the memory 108 may store a negative threshold referencewhich can be compared with the error signal in the comparator 110 tosense an abnormally low actual current. Occurrence of such an abnormallylow current indicates failure of the pumping system or associatedabnormalities, such as failure to load a delivery tube 36 in the device.Abnormal wall thickness of the tube 36 would also be detected by anabnormal phase of the pincher current spike waveform. Additionally,damaged cam surfaces or faulty bearings or motor would contribute toabnormal behavior and thus would be detected.

In the preferred embodiment of the present invention a bar code isadvantageously applied to the disposable administration set as a meansof directly transferring information regarding the disposableadministration set such as the pump stroke volume which relates to theamount of fluid displaced per revolution of the axle shaft, tubingdiameter, or the tubing wall thickness, from the disposableadministration set to the infusion device 11. This information may be,for example, directly applied to the disposable administration setduring the manufacturing process. Alternatively, the bar code mayprovide patient and medication specific information, relating to aparticular prescription being delivered, such as a dose/timespecification. This information likewise may be provided by a pharmacistwith the disposable administration set. Using this information, amicroprocessor can easily derive an appropriate shaft velocity. Thesensor may be optical, or magnetic or some other known technology.

What is claimed is:
 1. A method of shaping the contour of a cam tosqueeze fluid from a tube at a uniform rate, comprising:calculating thedifferential volume of said tube caused by an incremental decrease inthe width of said tube at each of plural tube widths; calculating theradius of a cam at each of plural, equally spaced angular positions, toprovide an incremental decrease in the width of said tube which, at thetube's current width, will provide identical differential volumes, andshaping the contour of said cam in accordance with the radius calculatedfor each of said plural, equally spaced angular positions.
 2. A methodof shaping the contour of a cam, as defined in claim 1, wherein saidradius calculating step comprises:solving the equation 2cdg-cg² -2k=0,where c=π/4 g=tube inside width d=tube relaxed inside diameter k=d² /4(number of increments).
 3. A method of shaping the contour of a camwhich will be rotated to predetermined, known angular positions within asingle rotation during successive, equal time periods to squeeze fluidfrom a tube at a constant rate, comprising:calculating the differentialvolume of said tube caused by an incremental decrease in the width ofsaid tube at each of plural tube widths; calculating the radius of a camat each of said predetermined, known, angular positions, to provide anincremental decrease in the width of said tube which, at the tube'scurrent width, will provide identical differential volumes; and shapingthe countour of said cam in accordance with the radius calculated foreach of said predetermined, know, angular incremlural, spaced angularpositions.